dose= 75 cGy per field (3600/24=150 which is divided by two because there are two fields=75)

75/(.996)(1.028)(.794)=92 MU

CSI was planned for a tall 12 year old with a treatment are 8x48 cm. The limits of the collimator, on the 100 cm isocentric linac, is 40x40cm. The min extended distance for this case is:
Part 2: what would the actual collimator setting be?

120 cm

40/100=48/x

40x=4800

x=120

Part 2: 6.7 x 40

we know that one side will be set for 40, we just need to know what the other will be: